java.lang.ArrayIndexOutOfBoundsException: -1 at java.util.ArrayList.get(ArrayList.java:324) at org.zkoss.zul.ListModelList.getElementAt(ListModelList.java:142) at org.zkoss.zul.Listbox.service(Listbox.java:3385) at org.zkoss.zk.ui.impl.DesktopImpl.service(DesktopImpl.java:691) at org.zkoss.zk.ui.impl.UiEngineImpl.execUpdate(UiEngineImpl.java:1123) at org.zkoss.zk.au.http.DHtmlUpdateServlet.process(DHtmlUpdateServlet.java:562) at org.zkoss.zk.au.http.DHtmlUpdateServlet.doGet(DHtmlUpdateServlet.java:457) at org.zkoss.zk.au.http.DHtmlUpdateServlet.doPost(DHtmlUpdateServlet.java:465)